"Just like 50,000 other people in the U.S. each year, this week I was diagnosed with stage 4 pancreatic cancer," Trebek said in the video. "Now normally the prognosis for this is not very encouraging, but I'm going to fight this, and I'm going to keep working, and with the love and support of my family and friends, and with the help of your prayers also, I plan to beat the low survival rate statistics for this disease.

"Truth told, I have to, because under the terms of my contract, I have to host Jeopardy! for three more years," he added. "So help me keep the faith, and we'll win. We'll get it done. Thank you."

Pancreatic cancer is the tenth leading site of new cancer cases, with 29,940 cases expected for men annually (compared to 174,650 estimated new cases of prostate cancer). So it’s still fairly rare, despite its prevalence rate increasing by about 1 percent per year between 2006 and 2015.

Trebek's diagnosis may have you wondering: What is stage 4 cancer, and is it always terminal?

What is stage 4 cancer?

The stage of a cancer is a way to describe how much cancer is in the body, so you know your treatment options and know how serious it is.

For pancreatic cancer, stages range from 0 (least serious) to IV (most). Tumor staging, when done from tumor tissue, is based on three key factors, including the size of the tumor and how far it has invaded the organ or body, whether it’s spread to lymph notes, and whether it has metastasized into other organs or to the bones. Stage four pancreatic cancer means the cancer has spread to other sites-it may or may not be in nearby lymph nodes.

Cancer staging is complex: It’s an important way to define what’s going on, but how the tumor behaves and the treatment required depends on many complex factors. Some tumors can be removed surgically, others can’t without major side effects.

Is it always terminal?

Each case and each person is different, so there's no specific way to know right away whether someone's stage 4 cancer is terminal or curable, or what their lifespan will be.